This project proposes to use an invasive microwave irradiation system to achieve local hyperthermia for the treatment of deep-seated cancers. Microwaves in the GHz range are characterized by short energy absorption lengths in living tissue. It is proposed that this characteristic will be exploited and the energy will be delivered directly to the tumor site through transmission lines and antenna structures which have been developed in our laboratory. Antenna probes with diameters less than 1 mm will be employed. Thus, implantation can be performed with minimal disturbance to the surrounding tissue, and many of the problems associated with the delivery of heat to deep-seated tumors will be circumvented. The objectives of this study are: (1) To further develop an invasive system for heating deep-seated tumors and to adapt the system for percutaneous insertion and surgical implantation so as to produce appropriate hyperthermia in difficult to heat, deep-seated tumors in humans; (2) to predict theoretically, and to measure experimentally, the heat distributions produced by the improved system in tissue phantoms, tumors and normal tissues of animals and humans; (3) to evaluate the therapeutic efficacy of the proposed system by studying the effect of the induced hyperthermia, alone, and in combination with ionizing radiation and chemotherapy on animal tumors, and in pilot clinical studies; and (4) to examine the effect of local hyperthermia on blood flow and the uptake of chemotherapeutic drugs in tumors and in normal tissues. These tumors will include transplantable mouse mammary adenocarcinoma (MTG-B), chemically induced tumors in the rat, and spontaneous brain tumors in dogs. The effects of the treatment on tumor cell viability will be assessed using the TD50 and tumor latency assays as well as histological evaluation. Tumor growth, TCD50 and host lifespan will also be studied as indicators of therapeutic effectiveness, and normal tissue response will be carefully observed in heated animals. Clinical tumors will include brain tumors and other tumors such as pancreas and prostate cancer.